1. Field of the Invention
The invention concerns a device for three-dimensional determination of the environment about a street vehicle, comprising a distance sensor which produces a series of two dimensional distance profiles, and a data processing unit and a storage unit which preprocesses and store sequential distance profiles, and produce a three dimensional image of the environment from a sequence of distance profiles. The invention further comprises a process for three-dimensional determination of the environment about a street vehicle utilizing such a device.
It is not possible today to survey the environment around a street vehicle since there are no suitable vehicle-adapted, high-resolution three-dimensional environment-scanning sensors. Depending upon the application, the first vehicle assistance systems to become available on the market will likely involve a comprise between the resolution of the sample data and the size of the surveyed area. So, for example, the radar system for an ACC application must be limited to a few degrees of scan horizontally, while for a parking assistance device the surveying of the environment ahead of, beside and behind the vehicle with ultrasound allows only a limited range and resolution to be realized. Video based systems offer a high resolution, however no distance information.
2. Description of the Related Art
From the field of robotics infrared scanners are known, which are capable of using articulated rotating mirrors to collect three-dimensional environmental information. For employment in street vehicles such sensors are however only suitable for limited purposes, since on one hand the complex mechanics are not sufficiently robust for the employment in practice for the most diverse street applications, and on the other hand, such sensors are relatively expensive owing to their complexity.
For this reason in the automobile sector laser scanners are primarily employed, which are designed to scan a thin disk (2D) within the three dimensional environment and to provide a depth profile of the surveyed sector. In DE 3932 720 A1 a distance measuring device is described for contactless recognition of distance and relative position of objects. The presence of an object is detected by means of a narrow bundled infrared beam and the distance is determined by an ultrasound device. U.S. Pat. No. 6,151,539 A1 shows an autonomous vehicle, which utilizes multiple laser scanners for object detection. Herein in particular a laser scanner is set up for monitoring the rear environment of the vehicle, in which the total theoretical detection area of 360° is divided, by not described means, into parallel overlapping environmental areas of respectively 180° and 30° for a so called quasi three-dimensional object detection.
Schneider (Schneider et al., “Millimeter Wave Imaging of Traffic Scenarios”, Intelligent Vehicles Symposium, Proc. IEEE, pp. 327-332) demonstrates the possibility of generating two-dimensional perspectives from three-dimensional data sets, here especially using a high-resolution radar system. The object therein is to classify vehicles on the basis of their two-dimensional view and to monitor their tracks, as well as to extract the street edge from the two dimensional view. A similar process to be employed in street vehicles for the recognition of a vacant driving space is also known from the subsequently published document DE 100 49 229 A1.
Systems for constructing three-dimensional environmental data on the basis of two-dimensional depth profile data taking into consideration the vehicle own movement are disclosed in documents U.S. Pat. No. 4,179,216 A1 and U.S. Pat. No. 4,490,038 A1 for the measurement of the profile of a railroad tunnel and the defect-free continuity of railway tracks, and, on the other hand, in U.S. Pat. No. 5,278,423 A1, systems are used in combination with the targeted application of pesticides and the determination of the extent of foliage within plantations. In all these systems a three-dimensional image of the environment is produced by the combination of a sequence of distance profiles using a data processing unit. In order to determine the spacing of the individual sequentially recorded profiles to each other, distance recorders are provided respectively in the wheels of the vehicle carrying the system.
A device for determining the position of an agricultural vehicle carrying a scanning sensor is described in U.S. Pat. No. 5,809,440 A1. Herein the track of the vehicle is followed by means of the global positioning system (GPS). Since the optical sensor used for recording plant growth however provides no distance information, the sequencing of the sensor information is able to produce only a two dimensional cartography of the environment.
In association with a street traffic scenario, a stationary system for determining and classifying vehicles passing the system is disclosed in U.S. Pat. No. 5,896,190 A1. Herein collected two-dimensional depth profiles from a laser scanner are combined for producing three-dimensional data. Therein the laser scanner is in a known fixed position above the vehicle roadway and monitors an area lying thereunder. Vehicles traveling through the scanned area are detected with sequential scans, from which the system sequentially extracts depth profiles. The speed information for correctly reconstructing a moving three dimensional traffic object from the two dimensional depth profile data is obtained by use of two light strata produced separately from the laser scanner. Therein the light strata are used in the sense of a light barrier for measuring speed, wherein entry of an object in the first light strata starts a clock and entry of the same object in the second light strata stops the clock. From the elapsed time and the known distance between both light barriers, the speed of the object can be calculated and therefrom a three dimensional image of the same can be constructed for the classification of the passing vehicle.
The devices known in the state of the art utilize, in reference to the aspect of the three dimensional determination of the environment, the analysis of static scenarios, such as inner walls of tunnels and the position of railroad tracks or the condition of the growth in fields or plantations. The three-dimensional image of the environment is not used therein in direct connection with actions of the sensor-carrying vehicles, but rather for documentation purposes or later statistical evaluation (determination of the growth density or planning of necessary repairs). Also, the device known from U.S. Pat. No. 5,896,190 A1 is essentially evaluated in a statistical scenario, in that a fixed point of a vehicular road is scanned or and locally occurring changes in condition (passage of vehicles) is detected and evaluated.